The specific aim of the proposed research is to further our understanding of the prenatal processes involved in the sexual differentiation of primates. We propose to accomplish this by investigating the influence of prenatal testosterone on the development of sexually dimorphic behaviors in Japanese macaques (Macaca fuscata). Female nonhuman primates that have been experimentally virilized with treatments of prenatal testosterone have served as useful models in investigations of congenital and drug-induced abnormalities of human sexual differentiation such as the adrenogenital syndrome (congenital adrenal hyperplasia) and progestin-induced hermaphroditism. The original organization hypothesis of sexual behavior was based on research involving rodents and juvenile rhesus monkeys. However, evidence for the same action on tissues that mediate adult sexual behavior is based on the performance of a single macaque. Moreover, these earlier studies on prenatally virilized rhesus macaques used animals reared under conditions that greatly restricted social experience. This may have delayed or disorganized the development of mature patterns of male sexual behavior. The existence of a large breeding group of Japanese macaques housed in an outdoor corral at the Oregon Regional Primate Research Center provides an excellent opportunity for a more naturalistic study on prenatal testosterone and sexual differentiation in primates. We have proposed, therefore, to implant pregnant females with testosterone propionate in Silastic capsules and to compare the behavior of the resulting androgenized female offspring with that of normal males and females.